In a hydraulic pump device configured to pump working fluid or lubricant fluid by a drive force generated by an internal combustion engine (vehicle drive source), an ejection capacity of the pump device varies depending on a rotational speed of the vehicle drive source. Therefore, there is a risk that a required hydraulic pressure could not be ensured due to insufficiency of the ejection capacity when the rotational speed of the vehicle drive source is low.
From a point of view of parts requiring the working fluid or lubricant fluid, there are a high-hydraulic-pressure required part to which a relatively high hydraulic pressure is required to be supplied and a low-hydraulic-pressure required part to which a relatively low hydraulic pressure is required to be supplied.
In a vehicle hydraulic system disclosed in JP2010-261509A in which the hydraulic pump device includes a main pump and also a sub pump, the working fluid is supplied to the high-hydraulic-pressure required part from both of the main pump and the sub pump when the rotational speed of the vehicle drive source is so low that the ejection capacity of the main pump is insufficient, and a supply destination to which the working fluid ejected from the sub pump is to be supplied is automatically switched from the high-hydraulic-pressure required part to the low-hydraulic-pressure required part when the rotational speed of the vehicle drive source is so high that the ejection capacity of the main pump is sufficient. Therefore, in the disclosed vehicle hydraulic system, the sub pump as well as the main pump supplies the working fluid to the high-hydraulic-pressure required part when the rotational speed of the vehicle drive source is low, and the sub pump supplies the working fluid to the low-hydraulic-pressure required part without supplying the working fluid to the high-hydraulic-pressure required part when the rotational speed of the vehicle drive source is high. Thus, when the rotational speed of the vehicle drive source is high, a load of the sub pump is reduced.